A common communication system transmits signals by loading the signals on high-frequency carrier waves. The signals are amplified or down-converted by a tuner at a receiving end, and subsequently demodulated by a demodulator. However, due to factors such as machinery aging or performance errors, the tuner becomes incapable of providing stable down-conversion to result in frequency offset along with time variations. In a conventional solution commonly used for frequency offset, a frequency offset is steadily estimated by iteration. However, in serious situations of channel fading and frequency offset, such conventional solution requires a relatively long period to conclude an estimated value, and is considered as rather limiting in actual practice.